It has been a long established fact that wiring and grounding inadequacies may result in many potential electrical vulnerabilities. In fact, a well known Electric Power Research Institute (EPRI) study in the 1990s stated that as much as 80% of power quality problems relate to inadequate wiring or grounding. Because of the frequency of wiring errors and the resulting potential for loss of life, property, product, and revenue, it is important to provide electrical energy users with capabilities that help determine unintentional (and even intentional) wiring errors that would have been otherwise overlooked.
There are several functions served by properly grounding an electrical system, some which are mentioned above. The National Electrical Code (NEC) and/or local electrical codes typically govern the general requirements for grounding and bonding of electrical installations. Some specific requirements include: 1) systems, circuits, and equipment required, permitted, or not permitted to be grounded; 2) circuit conductor or conductors to be grounded on grounded systems; 3) location of grounding connections; 4) types and sizes of grounding and bonding conductors and electrodes; and 5) methods of grounding and bonding.
Ultimately, these codes are intended to provide guidelines that facilitate the safety of equipment and personnel. Other objectives of suitable grounding configurations include providing a path for dissipating high energy electrical discharges, preventing static build-up, and establishing an equipotential voltage reference point for the electrical system. There are other important standards and guidelines that discuss wiring and grounding beyond those concerned with safety as they relate to equipment and personnel. The IEEE Emerald Book (IEEE 1100, Recommended Practice for Powering and Grounding Electronic Equipment) describes methods “to enhance equipment performance from an electric powering and grounding standpoint, while maintaining a safe installation as prescribed by national and local electric code requirements.”
An effective grounding path is defined by the NEC as “an intentionally constructed, permanent, low-impedance electrically conductive path designed and intended to carry current under ground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground fault detectors on high-impedance grounded systems.” A key aspect of this definition is that the ground path is meant to be used “under ground-fault conditions,” and not during steady-state operation. A primary reason ground paths are not meant to provide a return path for the current during steady-state conditions is that equipment may become inadvertently energized, posing a safety hazard to personnel. Another reason to avoid ground currents is the potential to introduce equipment interference problems into the electrical system.
The 2005 NEC Section 250.30(A)(1) states that “an unspliced system bonding jumper in compliance with 250.28(A) through (D) that is sized based on the derived phase conductors shall be used to connect the equipment grounding conductors of the separately derived system to the grounded conductor (neutral). This connection shall be made at any single point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices. The NEC allows for a single neutral-ground bond (connection) at the service entrance or at any separately derived system.”
FIG. 1 generally illustrates a properly bonded electrical system 10 having a utility service entrance 12, a main switchgear 14, a step down transformer 16 and a panelboard 18. Neutral (grounded) conductors 20 and grounding conductors 22 are provided for the components 12, 14, 16 and 18. FIG. 1 illustrates a “single” point of bonding 24 between the grounding conductors 22 and the grounded conductor 20 on each separately derived component (one at main switchgear 14 and the other at the step-down transformer 16).
FIG. 2 generally illustrates the electrical system 10 in FIG. 1 in an improperly (or “illegally”) bonded state. FIG. 2 illustrates a “single” point of bonding between the grounding conductor 22 and the grounded conductor 20 for each separately derived component as explained above in FIG. 1, but also has a bond 26 between the grounding conductor 22 and the grounded conductors 20 on the panel board 18. This additional neutral-ground (N-G) bond 26 at the panelboard 18 will allow current to circulate on the grounding conductor 22 during steady-state conditions creating both potentially hazardous electrical conditions and equipment operational issues.
What is needed, therefore, is a detection system to determine automatically the presence of potential improper grounded-grounding conductor configurations in an electrical power system. There is a further need for a system to determine automatically the location of improper grounded-grounding conductor configurations. There is also a need for a system that determines the absence of an expected grounded-grounding bond in an electrical power system. Aspects of the present invention are directed to fulfilling these and other needs.